BoilerFaultCodesYour boiler has switched itself off because it has become too hot internally and needs time to cool down before it can be used again.
Book a Gas Safe engineer within 24–48 hours. Your boiler may be unsafe or could break down completely if left.
Technical description: Boiler has exceeded the maximum temperature and needs to cool down
What causes this fault?
This fault occurs when the water inside the heat exchanger reaches an unsafe temperature, triggering a safety shut-off. The most common reasons are a pump failure that prevents water from moving, a blockage in the pipework, or a Build-up of limescale and sludge. Essentially, the boiler is generating heat but has no way to move it away into your radiators or hot water tank.
This fault is more common when the heating is first turned on after summer, as pump components can seize during long periods of inactivity.
DIY fix possible
Check that all radiator valves are fully open to allow water to flow.Wait 30 minutes for the unit to cool down completely.Press the reset button (indicated by a flame with a cross through it) on the front control panel.
Find a Gas Safe engineer
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Gas Safe Register →Protect yourself from future repair bills
A boiler cover plan would cover faults like F.20 — no call-out fees, no surprises.
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Vaillant Turbomax Plus 824/828E is discontinued — time for a new one?
Parts for discontinued models can be hard to find and expensive. A new A-rated boiler could save you money on both repairs and energy bills.
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